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A 21st-Century Water Forecast

By Felicity Barringer April 25, 2011 6:00 pmApril 25, 2011 6:00 pm

The broad-brush conclusion of a new federal report on the future impact of climate change on water in the West is a bit familiar. Throughout the West, there will be less snow, and what snow there is will melt faster. The dry Southwest is going to get drier, and the wet Northwest wetter, as a diagram in the report (above) shows.

The 122-page report includes original research — “including state-of-the-art climate modeling,” as Interior Secretary Ken Salazar said during a conference call on Monday — but also harks back to peer-reviewed scientific literature on seven river basins: the Columbia, the Klamath, the Sacramento-San Joaquin, the Colorado, the Missouri, the Truckee and the Rio Grande.

The report offers not just some interesting details on individual basins but a revealing window on how the administration of President Obama, who did not even mention climate change in his last State of the Union address, deals with the subject in general.

The report and the conference call send a clear message: the West is getting warmer, and while the effects vary depending on geography, the places that are feeling water stress now are going to feel more in the future because snow will melt faster, bringing a decline in summertime stream flows.

And as Mr. Salazar observed on Monday, this reordering of natural water supplies “will mean significant potential dislocations to the economy and the environment.”

The focus is largely on the impact of climate change, not the cause; the role of greenhouse gases is mentioned in a by-the-way context, in sentences like this: “It is widely accepted that water demand changes will occur due to increased air temperatures, increased greenhouse gas concentrations and changes in precipitation, winds, humidity, and atmospheric aerosol and ozone levels.”

This could be a coincidence or an early indication of a new administration strategy: deal with the immediate and palpable impacts of climate change, like water scarcity, first, and then tackle the overall problem later.

Certainly Mr. Salazar and two subordinates, Anne Castle, the assistant secretary for water and science, and Michael L. Connor, the commissioner of the Bureau of Reclamation, were intent on using the report, delivered in response to a 2009 Congressional mandate, to create or bolster a sense of urgency among Western water managers who are planning for the future.

For instance, while Mr. Salazar said there would be no change in nearly 80 years of compacts and court decisions that make up the what Colorado River water users call “The Law of the River,” he pointed out that the seven states and the federal government, joint managers of that system, “must realize that “on top of that already oversubscribed system you are looking at significant decreases in water supply.”

The report also had warnings for other river basins, noting for example that while the Upper Missouri River could expect a greater inflow of water over all in 60 to 80 years, the South Fork of the Platte River, on which the water-stressed city of Denver depends, is likely to get less.

And while the Columbia River system should be handling more runoff or snow melt over all in the future, in the low-flow summer months, “annual minimum-week runoff is projected to steadily decrease. Lower instream flows and increased summer air temperatures may result in warmer channel flow and possibly significant impacts on aquatic species and those species dependent on them.”

For the Rio Grande system, like the Colorado’s, the news is mostly bad for economies and environments that depend on readily available water. Runoff will increase when it is less needed, from December to March, and decrease in the April-July period when the need is far greater.

(An earlier version of this post incorrectly described the report as a joint effort by the Army Corps of Engineers and the Bureau of Reclamation. The Army Corps was not involved in its preparation.)

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How are climate change, scarcer resources, population growth and other challenges reshaping society? From science to business to politics to living, our reporters track the high-stakes pursuit of a greener globe in a dialogue with experts and readers.